#score {
    text-align: center;
}

h2 {
    text-align: center;
}

div {
    margin: 0 auto;
    width: 100px;
    height: 100px;
}

#main {
    width: 400px;
    height: 400px;
    background: white;
    border: 2px solid gray;
    margin: 0 auto;
    overflow: hidden;
}

#con {
    width: 100%;
    height: 400px;
    position: relative;
    top: -100px; /*隐藏最上层的那行*/
    border-collapse:collapse;
}
/* 行 */
.row{
    height: 100px;
    width: 100%;
}
/* 一个块 */
.cell{
    height: 100px;
    width: 100px;
    float: left;
}

.black {
    background: black;
}
.start {
    display: block;
    margin: 0 auto;
    margin-top: 20px;
    width: 150px;
    height: 50px;
    border: 1px solid white;
    border-radius: 10px;
    background-color: yellowgreen;
    line-height: 50px;
    text-align: center;
    color: #fff;
    font-size: 30px;
    font-weight: bold;
}